Small departures from standard that pass without consequence become the new standard, until they do not.
Vaughan's 1996 study of the Challenger decision. O-ring erosion was observed on prior flights, tolerated, and became the expected condition — so the launch decision was made against a standard that had already moved.
In practice
- A team that has skipped the pre-deploy check forty times without incident no longer regards skipping it as skipping anything.
- A ward that has run one nurse short for two years has redefined the establishment, and the staffing paper reports full compliance.
- Further reading
- Wikipedia
- Subject
- Risk & Reliability
- Essay
- How accidents actually happen